Home

Warning!

Make sure you are attempting to connect and drive valid GPIO pins for your board.

To run the example pull down the code:

 git clone [email protected]:Tpimp/QGpio.git  

Open the project file in QtCreator or manually edit the source files and then rebuild the project.

 qmake Gpio_Test.pro  
 make  

Run the application from QtCreator or start it from command line (sudo privileges may be required).

 ./Gpio_Test  

Keep in mind, the pins 199, 200, and 204 are specific to the Odroid-U3 I used for testing. Make sure to find the correct pin-out for your board and change the example to properly register the correct pins.

Using QGpio class and QGpioWatcher

(not officially supported by Qt Company or Qt SDK)

QGpioWatcher spawns a separate thread to monitor the registered pins. You might not need QGpioWatcher, if you only use output pins. Also, instead you can monitor the pins manually through a pulling method, or a custom event system (not covered here). Ideally your system handles GPIO pins in as interrupts. If you do use QGpioWatcher bare in mind:

• QGpioWatcher::THREAD_SLEEP_TIME must be created and initialized (in main preferably)

•  #include "qgpiowatcher.h"  
   #include "qgpio.h"  
   ...  
   // ~33.33 HZ sampling rate (30 milliseconds)
   int QGpioWatcher::THREAD_SLEEP_TIME = 30;
   ..  
   int main(int argc, char*argv[])  
   ...  
  

• after being created, the watch thread must be started before pins can be registered

•  QGpioWatcher gpio_thread;  
   gpio_thread.start();  
  

• Because Qt Application Event systems may contain critical shutdown - QGpioWatcher objects must be terminated before exiting.

•  QObject::connect(&app, &QGuiApplication::aboutToQuit, &gpio_thread, &QThread::terminate);  
   ... // before starting main event loop  
   return app.exec();  
  

• See the example application for more.

Because there are many gpio examples for sysfs (some even in C++), I will focus on the unique parts of QGpio.

Using it from QML

The C++ side:

 //registering QGpio type  
 qmlRegisterType<QGpio>("com.embedded.io",1,0,"QGpio");  

In QML:

 QGpio{  
     id:gpio200  
     number:"200";  
     onValueChanged: {  
       //pin200.color = (new_value? "green":"red");  
     }  
     Component.onCompleted: {  
       direction = QGpio.In;  
       edge = QGpio.Both;  
       active_low = false;  
       GpioWatcher.watchGpioItem(gpio200);  // QGpioWatcher was imported to QML Context
       list.model = GpioWatcher.exportedObjects();  
     }  
   }  

To find out more, check out Gpio_Test main.cpp.

I will continue improving GPIO integration. Next I plan to get PWM working, and if possible other software serial interfaces.